Background: In recent history, there have been significant increases in both soft drink consumption and the prevalence of obesity throughout the developed world. To help curb the obesity epidemic, a better understanding of the behaviors contributing to weight and fat gain is vital.

Objective: To examine the extent to which soft drink consumption is predictive of changes in body composition in middle-aged women over a 4-year period, while statistically controlling for age, energy intake, physical activity, and menopause status.

Design: A prospective cohort design over 48 months with no intervention. Self-reported soft drink consumption was used to predict changes in body weight and body fat percentage over the study period. Subjects included 170 healthy women (mean: 41.5 yrs at baseline). Soft drink consumption and menopause status were measured by questionnaire. Body weight was assessed using a calibrated, electronic scale, and total body fat percentage was measured using dual energy x-ray absorptiometry (DEXA). Energy intake was estimated using 7-day, weighed, food records.

Results: Women who primarily consumed sugar-sweetened soft drinks gained significantly more weight than those who consumed diet soft drinks or no soft drinks (p = 0.022), even after controlling for confounding variables, except energy intake, which weakened the relationship by 28%. Changes in body fat were unrelated to the type of soft drink consumed. Women who consumed 7+ soft drinks per week gained significantly less body fat (p = 0.015) and body weight (p = 0.052) over the 4-year study compared to women who consumed fewer soft drinks per week. Further investigation revealed that women who consumed 7+ soft drinks per week did so almost exclusively in the form of diet soft drinks (87%).

Conclusions: Drinking sugar-sweetened soft drinks significantly increases risk of weight gain compared to consuming diet soft drinks or no soft drinks over a 4-year period. It appears that this relationship is partly due to differences in energy intake among those who drink different types of soft drinks. Thus, it appears that consuming diet soft drinks or no soft drinks instead of sugar-sweetened soft drinks may be a worthwhile method of preventing weight gain.